Third generation partnership project (3GPP) mobile communication systems based on a wideband code division multiple access (WCDMA) radio access technology are widely spread all over the world. High-speed downlink packet access (HSDPA) that can be defined as a first evolutionary stage of WCDMA provides 3GPP with radio access technique that is highly competitive in the mid-term future. However, as requirements and expectations of users and service providers are continuously increased and developments of competing radio access techniques are continuously in progress, new technical evolutions in 3GPP are required to secure competitiveness in the future. Reduction of cost per bit, increase of service availability, flexible use of frequency bands, simple structure and open interface, adequate power consumption of a user equipment, and the like are defined as requirements.
Resource scheduling includes dynamic scheduling and persistent scheduling. The dynamic scheduling uses scheduling information which is allocated by exchanging control signals whenever data is transmitted or received. The persistent scheduling uses predetermined scheduling information to transmit or receive data.
FIG. 1 is a flowchart illustrating downlink data transmission employing dynamic scheduling. A base station (BS) transmits scheduling information to a user equipment (UE) through a downlink scheduling grant every time before the BS transmits downlink data. There is an advantage in that the BS can adequately schedule radio resources for the downlink data according to downlink channel condition.
FIG. 2 is a flowchart illustrating uplink data transmission employing dynamic scheduling. Radio resources are allocated through an uplink scheduling grant from the BS before the UE transmits uplink data.
FIG. 3 is a flowchart illustrating downlink data transmission employing persistent scheduling. The BS and the UE preconfigure radio resources before transmitting downlink data, and the BS transmits downlink data according to the preconfigured radio resources.
FIG. 4 is a flowchart illustrating uplink data transmission employing persistent scheduling. The BS and the UE preconfigure radio resources before transmitting uplink data, and the UE transmits uplink data according to the preconfigured radio resources.
VoIP (Voice over IP) is a service for transmitting voice data over IP (Internet Protocol) and provides voice data, which was conventionally provided in a circuit-switched (CS) domain, in a packet-switched (PS) domain.
In the CS-based voice service, end-to-end connection is maintained and voice data is transmitted, whereas in the VoIP, connection-less voice data is transmitted. Accordingly, the VoIP is advantageous in that network resources can be used very efficiently.
With the development of wireless communication technology, required capacity of user data is increased fastly. For an efficient use of network resources, existing CS-based services has been replaced with the PS-based services. The VoIP has been developed in this circumstance, and it is expected that most of the voice services is provided through the VoIP in the future.
A RTP (Real-time Transport Protocol) is developed so as to provide the PS-based voice services effectively. A RTCP (RTP Control Protocol) is a protocol for controlling the RTP. The RTP has time stamp information loaded on each packet and, therefore, can solve a jitter problem. An FER (Frame Error Rate) can be reduced through rate control by reporting the loss of RTP packets through the RTCP. In addition to the RTP/RTCP, a SIP (Session Initiation Protocol), a SDP (Session Description Protocol) and so on were also developed. It sustains end-to-end virtual connection, thereby solving a delay problem considerably.
FIG. 5 illustrates a traffic model at the VoIP.
Referring to FIG. 5, voice packets generated at the VoIP include packets generated in a talkspurt and packets generated in a silent period. For example, assuming 12.2 kbps AMR (Adaptive Multi-Rate), in the talkspurt, a RTP packet is generated at a cycle of 20 ms and has a byte size of 35 to 49, and in the silent period, a RTP packet is generated at a cycle of 160 ms and has a byte size of 10 to 24.
If a packet is generated at a constant cycle in a voice service such as VoIP, the size of a packet is relatively small and constant and, therefore, the persistent scheduling is generally applied. Radio resources are allocated persistently during configuring a radio bearer. Thus, packets can be transmitted or received even without exchanging control signals including scheduling information.
When data is transmitted or received according to the persistent scheduling, scheduling information is not provided and preconfigured radio resources are employed. If channel condition changes after configuring the radio resource under persistent scheduling, error rate can be increased.